Soil Temperature Field Research Articles

Simulation of Freeze–Thaw and Melting of Buried Ice in Longbasaba Moraine Dam in the Central Himalayas Between 1959 and 2100 Using COMSOL Multiphysics

AbstractPermafrost degradation increases the likelihood of glacial lake outburst floods on the Tibetan Plateau. Analyses of the freeze–thaw conditions in moraine dams and associated impacts on dam stability contribute toward reducing natural hazard risks. We used the heat transfer module of COMSOL Multiphysics to simulate the soil temperature field in the Longbasaba moraine dam, which is on the northern slope of central Himalaya. There is close agreement between the simulated and observed soil temperature values. Root mean squared errors (the square root of the mean of the square of all of the error) are below 1.30°C and mean bias errors vary from −0.10 to −0.52°C for the different soil layers. Between 1959 and 2020, active layer thickness increased at a mean annual rate of 0.024 m a−1. Under the Coupled Model Intercomparison Project Phase 6 scenarios, the buried ice inside the moraine dam is clearly melting. The maximum‐buried ice thaw depth is currently 3.4 m and at the end of the 21st century is projected to be 9.53, 16.69, and 21.83 m under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5, which indicates a continuous decrease in moraine dam stability.

Study on Temporal and Spatial Variation in Soil Temperature in Artificial Ground Freezing of Subway Cross Passage

Temperature is the fundamental variable used in artificial ground freezing (AGF) design to assess the frozen curtain’s state and carry out an analysis of its mechanical behavior. Therefore, it is important to appropriately understand the temperature variation in the soil during freezing and thawing throughout the construction process of AGF. In this paper, a soil physical state analysis model was established to obtain the one-dimensional distribution curve of the soil temperature field and the temperature variation curve of the soil with temporal, which can be used to explore the soil temperature characteristics during the construction of AGF, so as to scientifically evaluate the physical state of frozen soil and reduce the construction risk. The soil can be divided into three zones during the construction process of AGF, namely the frozen zone, the frozen fringe, and the unfrozen zone. Additionally, Hangzhou muddy silty clay was selected for the indoor model test to verify the correctness of the analytical model. The results show the following: (1) Due to the influence of the latent heat of the phase change, the physical state and temperature of the soil on both sides of the frozen fringe are not the same. It is not appropriate to use the same temperature index to judge whether the soil is frozen or thawed in the project. (2) For Hangzhou muddy silty clay, the freezing index is −1 °C, and the thawing index is 0.9 °C. The research results can provide some guidance for the judgment of the soil state during the AGF of subway cross passages.

Transportation of Mixed Hydrogen Gas in Buried Pipelines in Permafrost Areas

The application of existing gas transmission pipelines to deliver hydrogen-blended natural gas is the most operable method among many delivery methods. Hydrogen-blended natural gas with different hydrogen-blending ratios after passing through the throttling element is not the same. Using FLUENT to analyze the temperature variation after the Joule–Thomson effect for 0%, 5%, 10%, 20%, and 30% hydrogen mixing ratios. Workbench is used to analyze the soil temperature field around the pipeline and the stress displacement of the buried pipeline in the permafrost zone under different hydrogen mixing ratios. The analysis revealed that as the hydrogen mixing ratio increases, the temperature of the same point gradually increases after the Joule–Thomson effect, the low-temperature area around the buried pipe is gradually replaced by the high-temperature area, and the stress of the buried straight pipe also gradually decreases; while the maximum stress of the pipe initially decreases and then increases, and the displacement has no obvious change.

Numerical simulation and experimental validation on the heat transfer property of vertical buried tube ground heat exchanger

In order to study the effect of the arrangement of buried tubes on heat transfer, a three-dimensional heat transfer model of vertical U-shaped buried tubes is established. The regional thermal efficiency and soil temperature field around the buried tubes arranged in square array and rhombic array are numerically simulated. The numerical simulation results are compared with the experimental data to verify the correctness of the established model and simulation conditions. The results show that the rhombic arrangement form has more advantages than the square arrangement form: with the same number of buried tubes, the land use area of the rhombic arrangement form is smaller and the regional thermal efficiencies of the two forms are almost the same. The experimental validation shows that the experimental value of the average heat transfer rate of a single tube is in good agreement with the simulated value, and the relative error is 5.4%.

Outlet water temperature prediction of energy pile based on spatial-temporal feature extraction through CNN–LSTM hybrid model

Energy pile is a novel ground heat exchanger for ground source heat pump (GSHP) systems. Prediction of the energy pile outlet water temperature is essential for the efficient operation of GSHP systems. In this study, by establishing a convolutional neural network (CNN) and long short-term memory (LSTM) hybrid model (CNN-LSTM), the spatial-temporal feature of the soil temperature field (STF) was creatively considered to predict the outlet water temperature. The inlet and outlet water temperatures and the surrounding STF data of the energy pile were obtained through finite element simulation and used as the model training datasets. By building the CNN-LSTM model, the spatial-temporal features in datasets could be extracted, leading to more accurate prediction results than other benchmark models. For instance, the excellent prediction accuracy of CNN-LSTM is reflected by an average R2 value of 96.252%, which is higher than the values of the LSTM, CNN, ANN, and SimpleRNN models by 2.326%, 3.527%, 4.585%, and 5.755%, respectively. Furthermore, the influence of different STF datasets on the prediction accuracy was investigated. The corresponding dataset acquisition method based on the optimized sensor arrangement scheme was proposed, which can improve the information extraction performance of the CNN-LSTM model.

Temporal and Spatial Evolution Law of the Freezing Temperature Field of Water-Rich Sandy Soil under Groundwater Seepage: A Case Study

We aimed to assess the temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil in underground freezing engineering, taking the newly built west ventilating shaft freezing engineering in the Yuandian No. 2 Mine of Huaibei Coalfield as the engineering background. The influence of groundwater seepage on the freezing temperature field was qualitatively analyzed using field measured data. Based on the mixture medium theory, a hydrothermal coupling numerical calculation model of the freezing temperature field was established. The temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil was obtained via the analysis of field measured data and numerical calculation results. It was found that the proportion of water that froze into ice in the soil mass within the freezing pipe circle is more than that outside of the freezing pipe circle; thus, the phase change in the soil mass within the freezing pipe circle is highly obvious. Groundwater seepage has an “erosion” effect on the upstream and side frozen walls and a “cooling superposition” effect on the downstream frozen wall. Under the effect of groundwater seepage of 2.81 m/d, the average temperature of the effective frozen wall during excavation is below −15 °C, while the thickness is above 5 m for the selected sandy layer at the site, meeting the construction and design requirements. When the groundwater flow rate increases from 0 to 10 m/d, the closure time of the frozen wall increases from 27 to 49 days, an 81.48% increase; the upstream thickness of the effective frozen wall decreases from 5.635 to 4.65 m, which represents a 17.48% decrease, while the downstream thickness increases from 5.664 to 7.393 m, an increase of 30.60%. The numerical calculation model in this paper can be used to predict the development law of the freezing temperature field of the water-rich sandy layers in the Yuandian No. 2 mine and to adjust the on-site cooling plan in real time according to the construction progress. This study provides some theoretical basis and reference for the construction and designs of the freezing temperature fields of water-rich sandy soil layers.

Experimental and numerical investigation on heat transfer characteristics of vertical ground heat exchangers in karst areas

Heat transfer between the ground heat exchanger and surrounding stratum under the action of groundwater seepage is a potential problem in karst areas, few systematic studies on it have been carried out yet. A model test apparatus was built to experimentally investigate the effects of karst groundwater seepage and ground stratification on the heat transfer characteristics of ground heat exchangers. The heat and seepage transfer coupling model for ground heat exchangers was established, and verified with the measured data from the model test. Base on the model, the influence of seepage velocity and direction on the heat transfer of ground heat exchangers was analyzed and discussed. Test results show that the seepage can promote the temperature field around the heat exchanger to reach the steady state faster, and the influence of seepage on the soil temperature field around the heat exchanger increases with increasing the seepage velocity. The seepage will carry the heat released by the heat exchanger from the upstream side to the downstream, which effectively reduce the accumulation of heat around the heat exchanger. Soil boundary exists the sudden change of temperature when there are great differences in thermal properties between adjacent soil layers, which can be attributed to the influence of ground stratification. The numerical model proposed in this study can well predict the distribution of soil temperature field around heat exchangers in the model test. Simulation results show that the temperature of soil around the heat exchanger will change along the seepage direction.

Modeling the Temperature Field in Frozen Soil under Buildings in the City of Salekhard Taking into Account Temperature Monitoring

Most residential buildings and capital structures in the permafrost zone are constructed on the principle of maintaining the frozen state of the foundation soils. The changing climate and the increasing anthropogenic impact on the environment lead to changes in the boundaries of permafrost. These changes are especially relevant in the areas of piling foundations of residential buildings and other engineering structures located in the northern regions since they can lead to serious accidents caused by the degradation of permafrost and decrease the bearing capacity of the soil in such areas. Therefore, organization of temperature monitoring and forecasting of temperature changes in the soil under the buildings is an actual problem. To solve this problem, we use computer simulation methods of three-dimensional nonstationary thermal fields in the soil in combination with real-time monitoring of the temperature of the soil in thermometric wells. The developed approach is verified by using the temperature monitoring data for a specific residential building in the city of Salekhard. Comparison of the results of numerical calculations with experimental data showed good agreement. Using the developed computer software, nonstationary temperature fields under this building are obtained and, on this basis, the bearing capacities of all piles are calculated and a forecast of their changes in the future is given. To avoid decreasing the bearing capacity of piles it is necessary to prevent the degradation of permafrost and to supply the thermal stabilization of the soil. The proposed approach, based on a combination of the soil temperature monitoring and computer modeling methods, can be used to improve geotechnical monitoring methods.

Simulations and Experiments of Soil Temperature Distribution after 2.45 GHz Long-Term Microwave Treatment

Soil disinfection is an important agronomic measure to prevent soil-borne diseases, insects, weeds and other hazards. Based on the premise of being environmentally friendly, microwave soil disinfection can improve crop yield and quality in a pollution-free, residue-free and green way. The law of microwave soil heating is the theoretical basis of microwave soil disinfection. Therefore, in this paper, loess soil of North China and black soil of Northeast China are used as test materials to explore the law of soil heating under the action of microwaves. First, COMSOL Multiphysics software was used to simulate the temperature field change in the microwave-irradiated soil, and a simulation model of the temperature field of the microwave-irradiated soil was constructed to analyze the effective working range and temperature distribution characteristics of the microwave-irradiated soil. Second, using the 2.45 GHz microwave treatment, the following conditions were tested: soil moisture conditions of 10%, 15%, 20% and 23% (within the natural moisture content range). The loess and black soil were treated by microwave irradiation for 1~12 min, respectively (1 min/time increment). A single-factor experiment was designed to explore the influence of these factors on the soil heating law. The results show that the two soil surface temperatures are positively correlated with the soil moisture content, both of which satisfy Tsurface23% > Tsurface20% > Tsurface15% > Tsurface10%, and the surface temperature of black soil is higher than that of loess. According to the experimental results of the internal temperature distribution of loess and black soil irradiated by microwaves, the surface equations of “irradiation time–soil depth-soil temperature” and “irradiation time–soil moisture content–soil temperature” were constructed by surface fitting. When the irradiation time and moisture conditions are the same, the average temperature inside the irradiation area satisfies T¯α black soil > T¯α loess. The results of long-term microwave soil heating preliminarily confirmed the feasibility of microwave soil disinfection and the optimal conditions of microwave irradiation in loess of North China and Northeast black soil, which provides a certain reference for the study of soil-borne diseases inactivation at high temperature.

Spatial variation of soil temperature fields in a urban park

Soil temperature is the most important factor that regulates the rate of physical, chemical and biological processes in the soil. A peculiarity of the urban environment is the occurrence of “heat islands”. The increased temperature of urban environment significantly changes environmental conditions and contributes to the activation of phenomena that lead to the acceleration of global climate change. The aim of the work is to reveal the patterns of spatial variation of soil temperature in a city park at the different scale levels. Soil temperature was measured on a regular grid with different lags between measurement points. The measurement results were processed using geostatistical methods to quantify the spatial process at different scales. The results obtained allowed to quantify the patterns of spatial variability of temperature fields at different hierarchical levels. Scale-dependent effects of soil temperature variation were identified. The role of stand density, litter depth, and soil moisture on soil temperature variation was found. The results of the study are the basis for developing an optimal soil temperature measurement plan for environmental monitoring purposes. Suggestions were also made for the management of park stands in order to reduce the temperature load. The spatial variation in soil temperature demonstrates the occurrence of scale-dependent patterns. The spatial organization of temperature fields must be taken into account for optimal environmental monitoring and urban environmental management strategies. The soil temperature regime is characterised by a significant level of stability compared to air temperature. The soil temperature fields in an artificial park plantation are characterized by spatial patterns of a complex nature. The temperature field presents a spatial component that is invariant to time. It is most likely that the spatial variability of soil properties induced by natural factors and recreation are the cause of the generation of this pattern. Also in the soil temperature field there is a spatial pattern, which reflects the different sensitivity of the soil to the seasonal trend of temperature change. The generation of this pattern is due to the different insulating capacity of the forest litter in the park plantation. The results obtained point to the important role of leaf litter as a factor in the dynamics of the soil temperature regime. It is hypothesized that leaf litter in the park contributes to the enhancement of carbon sequestration during winter time.

Study on Temperature Field Evolution and Frozen Wall Closure Judgment Criteria of Inclined Shaft under Inclined Holes Freezing Condition

A similarity experiment study is conducted to investigate the evolution characteristics of temperature field and frozen wall closure judgment criteria for the inclined shaft, under inclined holes freezing condition using an adjustable-angle freeze sinking analogous instrument. The changes of temperature and frozen wall thickness with the freezing time in the inclined shaft section, are recorded in real time, and the water pressure of axial and radial hydrological holes are measured. The results demonstrate that the soil temperature change can be divided into three stages under the conditions of salt-water temperature of -32°C and flow rate of 3.18 m/s: rapid cooling before reaching the freezing point, slow cooling in the process of freezing latent heat release, and accelerated cooling and stabilization after freezing latent heat release. The distance from the freezing pipe is the main factor affecting the freezing wall temperature. Affected by the arched arrangement of frozen pipes, the freezing speed in the position of arch crown and arch baseline is slower than the position of wall corner and base plate. A new judgment criterion of frozen wall closure based on the water pressure of the axial hydrological pipe is recommended. In all, this paper has an enlightenment significance for understanding the evolution of the soil temperature field, and predicting the frozen wall closure time in applications of the inclined holes freezing method for the inclined shaft.

COMSOL Modeling of Heat Transfer in SVE Process

Non aqueous phase liquid (NAPL) pollution exists in porous media such as soil. SVE technology can be used to remove this pollution in soil. However, few domestic and international studies have paid attention to the changes of soil temperature in the field, which we believe can be useful information to optimize the layout of heating wells. In this research we established partial differential equations of soil heat transfer using the COMSOL multi-field coupling tool to simulate the field distribution of the change in soil internal temperature in the process of SVE to obtain the change of effective heating area with time under certain initial heating conditions. At the same time, we used liquid ethylbenzene to represent NAPL pollutants, and designed a simulation of soil temperature field distribution under the movement of liquid ethylbenzene under external pressure. It was found that under the action of Darcy’s velocity field, the utilization efficiency of the SVE system for the heat source was significantly improved, that is, the temperature distribution of the soil was more uniform. However, the temperature of the heated area increased slowly because the extraction well took away the heat energy. The heat source power should be increased or prolonged to improve the effect of Darcy’s field. Through a coupled simulation, we obtained a variation relationship of the soil temperature field in 1800 min under the action of one extraction well and four heating wells. These data will provide the basis for our next step in designing an algorithm to optimize the distribution of heating wells.

Impact of Isothermal Layering on the Stability of Saline Soil Subgrade in Cold Regions

In order to determine the influence of heat on the stability of the saline soil subgrade slope in cold regions. Firstly, four typical representative saline soils were selected as subgrade fillers, and geotextiles were added at the bottom of the subgrade as a study subject. A two-dimensional numerical model for the temperature field of subgrade soil was established based on COMSOL Multiphysics. Secondly, combined with the main strength parameters of subgrade soil at different temperatures, an isothermal stratification-strength parameter function calculation model was proposed. Then, the SLOPE/W module in GeoStudio is used to stratify the established subgrade model according to isotherms and calculate the stability safety factor of saline soil subgrades in cold regions under different months, slopes, and subgrade heights, respectively. Finally, the influence of submergence at the foot of the slope on the stability of the subgrade slope is discussed. The results show: After the cold season coming, with the decreasing of temperature, the stability of HC-1 and HC-2 saline soil subgrade slope increased to different extents when the ground temperature dropped to -10°C. When the local temperature dropped below -10°C, the stability has slight decline; CS-1 and CS-2 saline soil subgrade in the ground temperature dropped to 10°C (HC-1 and HC-2 denote two groups of saline soil with high chloride-salt content (≥15%) and low sulfate salt content (≤0.5%), whereas CS-1 and CS-2 denote two groups of saline soil with low chloride-salt (≤5%)), the slope stability was significantly improved, and the stability of CS-1 increases slightly with further decrease in temperature.

Experimental and Numerical Study of an Active Solar Heating System with Soil Heat Storage for Greenhouses in Cold Climate Zones

Root temperature is an important ecological factor affecting plant growth. A solar greenhouse with an active solar heating system was built in Jinan, in the cold climate zone of northern China. Experiments encompassing the complete cycle of heat collection, heat storage, and heat release were carried out. Using the experimental data, the numerical simulation of soil heat storage with a variable heat flow was executed using the ANSYS (ANSYS Inc., Pittsburgh, PA, USA) Fluent software. Soil temperature fields were studied on typical sunny days and typical cloudy days in the transition season and winter. The solar collector efficiency and coefficient of performance of the system were investigated. The applicability of this active solar soil heating system with soil heat storage for cold areas was evaluated. The results showed that the system effectively maintained suitable ground temperatures to prevent plant growth inhibition caused by low ground temperatures in winter. During the experimental period, the solar collector efficiency was 47% and the system’s coefficient of performance was 67.70. The thermal performance of the system was much better than a traditional energy system. This study showed that this active solar heating system with soil heat storage is an economic and feasible way to increase soil temperatures in solar greenhouses in cold areas.

Analysis of the thermal process of hot oil pipeline shutdown and restart

For a long transport pipeline in service in the east, the thermodynamic change rules along the pipeline during shutdown and restart were simulated and analyzed respectively, and the characteristics of soil temperature field during restart were clarified. The change of the dangerous section position was analyzed emphatically, and the reasonable shutdown time was determined according to the temperature of the dangerous section position. The research of this paper can provide theoretical support for the determination of shutdown time in the process of shutdown.

Dimensionless analysis of soil temperature field of shallow subway tunnel

For evaluating the long-term heat storage capacity of a shallow subway tunnel's soil layer, a dimensionless mathematical model is established based on the heat conduction of tunnel surrounding rock. Using the finite volume method, the heat balance equations of the dimensionless internal and boundary elements for the soil temperature field are solved numerically. An analysis of the evolution of soil temperature field and tunnel wall temperature with time is presented in this paper. A long-term heat exchange results in a significant coupling superposition effect between the atmospheric air temperature disturbance domain and the subway air temperature influence domain in the subway tunnel. In addition, a simple calculation method for the unstable heat transfer criterion is provided by looking at a chart, and the long-term heat storage capacity of tunnel surrounding rock can be determined quickly. An engineer can use this method to expeditiously design the environmental control system of a subway tunnel.

Measurement and Analysis of Soil Temperature Field Based on Fiber Bragg Grating Sensor Array

Studying the soil temperature field and its variation law is of great significance to the real-time service of agricultural production. To solve the problems of low detection efficiency and difficulty of distributed detection, a distributed detection method of soil temperature field using wavelength division multiplexing and space division multiplexing technologies based on fiber Bragg grating (FBG) sensor is proposed. In this scheme, the stainless steel tube encapsulating the FBG string was vertically buried in the measured soil, and the tunable laser method and the peak-seeking algorithm were used to demodulate the wavelength of each sensor of the FBG string. The soil temperature field measurement experiments were carried out in the farmland environment. The experimental results show that the proposed method can detect the soil temperature field in real time. The internal temperature of soil changes periodically with the periodic change of surface environment temperature. With the increase of depth, the influence of surface temperature on soil temperature gradually decreases, and the amplitude of soil temperature oscillation gradually decreases, but the hysteresis effect of temperature peak becomes more and more obvious. The ambient wind speed can reduce the temperature of soil surface and shallow layer. Soil moisture affects the speed of temperature transfer from the surface layer to the deep layers, and the hysteresis effect of temperature peak is more significant in the soil with higher moisture. Solar radiation has a great influence on the temperature of soil surface and shallow layer.

生物质发酵产热-小型温室棚联用对春冬季烟苗生长温度调控的数值研究

PDF HTML阅读 XML下载 导出引用 引用提醒 生物质发酵产热-小型温室棚联用对春冬季烟苗生长温度调控的数值研究 DOI: 10.5846/stxb202106211652 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中国烟草总公司重庆市公司科技项目（NY20190401070012） Numerical study on temperature control of tobacco seedlings in spring and winter using a biomass fermentation heat production-small greenhouse combination Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:小型温室棚作为农业生产的重要设施，可为农作物创造一个温度适宜的、受保护的生长空间，保证作物正常生长、促进作物早熟。以确保重庆地区春冬季烟苗正常发育、维持温室内适宜的土壤温度为导向，对温室棚内温度进行了试验和数值模拟，探究了温室棚内温度分布规律，并在此基础上分析生物质发酵产热对温室棚内土壤温度场的影响。结果表明：试验中埋设稻壳的温室棚内土壤温度平均提高3.5℃且温室棚中平均温度低于10℃的天数明显减少。埋设稻壳的温室棚中烟苗茎高和叶片数增长值最大，平均茎高从移栽时的7.8 cm增长到了12 cm，叶片数从平均5片增长到了11片，均大于未埋设稻壳试验组，这表明土壤中埋设稻壳有助于烟草的生长发育。数值研究表明温室棚内不同深度的土壤层温度变化状况一致，均呈现先降低后升高再降低的趋势。地温随土壤深度的增加而降低，地表下10 cm、20 cm的土壤层区域温度高于10.6℃、8℃，有利于烟苗在低温环境下正常生长。且土壤温度存在一定的昼夜温差，更利于烟苗发育。埋设稻壳的温室土壤层温度变化趋势与未埋设稻壳的温室一致，但其土壤层平均温度、最低温度至最高温度以及昼夜温差分别升高了2.3℃、1.1-5.5℃、4.8℃。试验和数值研究结果表明稻壳发酵产生的热量可以提高和维持温室内土壤温度，对土壤具有保温和热量补给的作用。 Abstract:As an important facility for agricultural production, small greenhouses can create a protected growing space with suitable temperatures for crops to ensure normal growth and promote early crop maturity. In this study, the aim is to ensure the normal development of tobacco seedlings in spring and winter in Chongqing and to maintain a suitable soil temperature in the greenhouse. Experiments and numerical simulations of greenhouse shed temperatures were carried out to investigate the temperature distribution pattern inside the greenhouse. On this basis, the effect of heat production from biomass fermentation on the soil temperature field in the greenhouse was also analyzed. The results showed that the soil temperature in the greenhouses with buried rice hulls increased by an average of 3.5℃ and the number of days when the average temperature in the greenhouses below 10℃ was significantly reduced. The largest increases in stem height and leaf number of tobacco seedlings were observed in the greenhouses with rice hulls. The average stem height increased from 7.8 cm at transplanting to 12 cm and the average number of leaves increased from 5 to 11, both of which were greater than in the experimental group without rice hulls. This indicates that the burial of rice hulls in the soil was beneficial to the growth and development of tobacco seedlings. The numerical study showed that the temperature of the soil layers at different depths in the greenhouse shed varied consistently, all showing a trend of decreasing, then increasing, and finally decreasing. The ground temperature decreased with the increasing soil depth. The temperature of the soil layer 10 cm and 20 cm below the surface was higher than 10.6℃ and 8℃, which was conducive to the growth of tobacco seedlings. And there existed a certain diurnal temperature difference in soil temperature, which was more beneficial to the development of tobacco seedlings in low temperature environment. The trend of soil temperature in the greenhouse with buried rice hulls was same as that in the greenhouse without buried rice hulls, but the average temperature, the minimum to the maximum temperature, and diurnal temperature differences in the soil layer increased by 2.3℃, 1.1-5.5℃, and 4.8℃, respectively. The results of experimental and numerical studies showed that the heat generated by the fermentation of rice hulls could raise and maintain the soil temperature in the greenhouse, providing insulation and heat recharge to the soil. 参考文献 相似文献 引证文献

Investigating Soil Desiccation Cracking Using an Infrared Thermal Imaging Technique

AbstractSoil desiccation cracking is of great concern in many fields such as hydrology, geology and agriculture, whereas its multi‐physical governing mechanism remains unclear up to now. As evaporation is a key influencing factor to soil cracking, capturing the evaporation‐induced soil temperature will significantly contribute to the improved understanding of soil cracking behaviors. Infrared thermal imaging enables the surface temperature measurement through converting infrared radiation into visible images, and has not been applied for soil cracking characterizations in the past. In this study, the fundamental mechanisms of soil desiccation cracking are investigated through the combined usage of three noninvasive techniques including infrared thermal imaging, particle image velocimetry, and digital image processing. Experimental results reveal the correlation between the evaporation‐related temperature of soil and its hydro‐mechanical behaviors. The evaporation rate is proportional to the soil‐atmosphere temperature difference. The soil body with a higher water content corresponds to a larger temperature difference, with the more apparent correlation observed in the unsaturated state of soil. Furthermore, as indicated in a nonuniform soil temperature field, the pore water migrates from the soil body with high temperature into the body with low temperature, similar to the soil particle motion under drying. Hence, the soil body with low temperature attracts additional water to maintain a high water content, resulting in a fast evaporation rate and a low temperature field for a long time. The evolution of the desiccation crack network is also related to the temperature distribution. Soil desiccation cracks tend to form in a lower temperature area, whereas the soil body with a higher temperature presents a more remarkable volume shrinkage. Primary cracks (defined as those first to develop and cause the breaking up of the intact material into separate clods) propagate along the isotherm, while the propagation path of secondary cracks (defined as those sub‐cracks initiated from primary cracks and subdivide soil to smaller clods) is first orthogonal to the isotherm and then rotates to gradually overlap with the isotherm. This study highlights the potential application of the infrared thermal imaging technique to investigate the underlying mechanisms of soil‐atmosphere interaction and perform soil desiccation cracking prediction.

Study on the evolution characteristics of temperature and heat storage of the soil surrounding the tunnel with years

The thermal energy performance of subway tunnel plays a key role to guarantee the operation safety of train. Most of the previous research focused on the air temperature in tunnel, but neglected the temperature of surrounding soil. This study investigated the energy performance, i.e., heat absorption and release, and spatial and temporal change of the soil temperature around subway tunnels by reduced-scale experiments with validated CHAMP-BES CHAMPS-BES (Coupled Heat, Air, Moisture and Pollutant Simulation in Building Envelope Systems) simulations. On the one hand, the experimental results showed that the soil temperature reached a dynamic balance in 10th year. The semi-infinite soil surrounding the tunnel is beneficial to control the tunnel air temperature in first 10 years. On the other hand, considering the influence of soil property parameters and types on soil temperature field, the small density, small specific heat capacity and large thermal conductivity of tunnel surrounding soil was recommended on design of subway tunnel due to the great heat storage capacity. The sandstone has the best heat storage capacity. The results showed that the heat storage of per cubic meter sandstone surrounding the tunnel in Southwest China is 71% more than that of clay in South China within 20 years. Therefore, choosing Sandstone as the soil surrounding the tunnel was recommended for practical engineering. This work not only contributes to the safety and reliability of the subway’s operation, but also provides theoretical foundations for the temperature control in the tunnel, benefiting the energy conservation of the train air conditioning systems both in the train and in the subway station.